Micro devices manufacturing method and apparatus therefor

ABSTRACT

An exposure method according to the present invention includes a first step of forming on a substrate an alignment mark including a concave and convex pattern; a second step of forming a coat over said alignment mark and the other area on said substrate; a third step of flattening said coat; and a fourth step of applying a photosensitive material on said coat flattened by said third step and projecting a mask pattern thereto. The alignment mark is formed by said concave and convex pattern arranged with a pitch which is smaller than the predetermined value between adjacent convex portions having a width of not less than a predetermined value.

This application is a division of prior application Ser. No. 09/192,439filed Nov. 16. 1998, which is a continuation of prior application Ser.No. 08/759,326 filed Dec. 2, 1996 now abandoned; which is a divisionalof Ser. No. 08/457,232 filed Jun. 1, 1995, now U.S. Pat. No. 5.601,957.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a micro device manufacturing method andan apparatus therefor, and in particular, to an exposure method and asubstrate polishing apparatus in manufacturing micro devices such assemiconductor devices, liquid crystal display devices, etc.

2. Related Background Arts

In the case where micro devices such as semiconductor devices, liquidcrystal display devices and the like are manufactured, there has usuallybeen used an exposure apparatus which exposes a pattern formed on areticle (or a photo mask and the like) onto a shot area on a wafer (or aglass plate and the like) on which a photosensitive material is applied.For this kind of exposure apparatus, an exposure apparatus of aso-called step-and-repeat type has been frequently used which repeatoperations of sequentially exposing the pattern on the reticle onto theshot area on a wafer. Recently, there has been developed a projectionexposure apparatus of a so-called step-and-scan type which exposes thepattern on the reticle onto an area wider than an exposure field of anprojection optical system by scanning the reticle and the wafer at thesame time.

Incidentally, since, a semiconductor device is, for example, produced bysuperimposing a plurality of layers of circuit patterns on the wafer,when circuit patterns of a second layer or a later layer are exposed onthe wafer, alignment of each shot area of the wafer already formed withthe circuit pattern with the pattern image of the reticle, that isalignment of the wafer with the reticle, must be precisely performed.For this purpose, there has been usually adopted a method wherein one ormore wafer masks for alignment are formed on the wafer together with thereticle pattern and the wafer marks are used for aligning the circuitpatterns of a subsequent layer.

There are several alignment sensors used for measuring the position of awafer mark, which systems include an LSA (Laser Step Alignment) systemwhich measures the position of a mark by irradiating a laser beam to awafer mark on a wafer and detecting a diffracted and/or diffused light,an FIA (Field Image Alignment) system which measures the position of thewafer by image processing the wafer mark illuminated by a light emittedby a halogen lamp and having a wide wavelength band width, or an LIA(Laser Interferometric Alignment) system which measures the position ofthe wafer mark by irradiation with bi-directional laser beams, thefrequencies of which are slightly different, causing two diffractedbeams to interfere with each other and then detects the phase of theinterfered beams. Of these systems, the LIA system conforms; to aflattening technique explained hereinafter, since it is most effectiveto detect the position of the wafer mark on the wafer which has a roughsurface or a surface difference in level which is small.

Incidentally, the shape, number or size of the wafer mark for alignmentis selected in correspondence with resolution of the projection opticalsystem of the exposure apparatus, a required accuracy in alignment, acondition of the layer on the wafer, etc. There have usually been usedmany kinds of shapes, such as slit-like shape, dot-like shape orcross-like shape. However, in the past, most of these wafer marks havehad relatively large recesses or concave portions; (having 4 μm width, 6μm width and the like) and are formed with a concave and convex pattern,said pattern being periodically arranged between adjacent convexportions.

Multi-layer interconnection is a requisite of high integration and highdensification as seen in a super LSI. In this technology, a techniquefor flattening the surface of a film or membrane of a predeterminedlayer is very important. This flattening technique is indispensable notonly for realizing multi-layer interconnection but also for a process ofproducing an integrated circuit of the multi-layer structure. Such aflattening technique is usually performed by a chemical method such asan anodic oxidation method, a resin coating method, a glass flow method,an etch back method, a lift off method, a bias spatter method and thelike. However, in addition to the above methods, a process (a chemicaland mechanical polishing process) for chemically and mechanicallypolishing the surface of the film formed on the substrate by the abovementioned method is practiced as occasion demands.

A general structure of a substrate polishing apparatus for polishing thesurface of a film on the substrate is shown in FIG. 12. In FIG. 12, awafer 124 is held by vacuum suction by means of a vacuum suction table125 with a surface 124 a (hereinafter referred to as pattern formationsurface) on which a pattern layer and an upper layer film or membraneare formed. The wafer 124 held by vacuum suction on the vacuum suctiontable 125 is rotatable in the direction of rotation 300B of a rotarytable 136, since the vacuum suction table 125 is placed on a rotarytable 126 which can rotate in one direction.

A polishing surface plate 122 having a polishing pad 123 is disposed ata position that faces with the pattern formation surface 124 a of thewafer 124 on the suction table 125. The polishing pad 123 rocks oroscillater in the same direction as the movement of a rocking table 121,since the polishing surface plate 122 is held by the rocking table 121.

Moreover, a polishing agent supplying nozzle 127 for supplying apolishing agent to the pattern formation surface is provided. Thepolishing agent is supplied by the polishing agent supplying nozzle 127between the pattern formation surface 124 a and the polishing pad 123,and at the same time at least one of the vacuum suction tables 125 andthe polishing surface plate 122 moves upward and downward direction 300Ato cause the polishing pad 123 moving in response to rocking movement ofthe rocking table 121 and the wafer 124 rotating in response to therotation of the rotary table 126 to contact, thereby polishing thepattern formation surface 124 a (the upper most film formed on the upperlayer of pattern layers) on the substrate 124.

However, when the flattening process is performed by chemical andmechanical polishing, a phenomenon of so-called dishing which creates adish-like concave portion or depression on the surface of the film ormembrane results, if there is one or more concave portions or recesseshaving a width of not less than 2 μm on an under layer pattern of ametallic film or membrane which is beneath the film to be flattened.Accordingly, a same phenomenon such as stated above will occur on thesurface of the membrane formed on a concave and convex pattern, if thewafer mark has relatively large concave portion (4 μm width, 6 μm widthand the like) like a conventional wafer mark and if they are formed onlyby periodichally arranged concave and convex patterns. A state of thedishing is shown in FIGS. 8(a) and 8(b).

FIG. 8(a) shows a state wherein an oxide film or membrane 92 is formedon a substrate 93 such as a wafer and recess or concave portion 90 a hasbeen formed in the oxide film by an etching, thereafter, a metallic coat91 is formed on the oxide film by a spattering of aluminum. FIG. 8(b)shows the state wherein said chemical and mechanical polishing isthereafter practiced on a product shown in FIG. 8(a). In FIG. 8(b) adish-like portion D1 is created by dishing above the concave portion 90a when the width of the concave portion 90 a is not less than 2 μm.Dishing as shown in FIG. 8(b) is caused when a pattern in which aplurality of concave portions or recesses 90 b are periodically arrangedis formed on a substrate and the metallic coat 91 is coated on thepattern. In this case, if a chemical and mechanical polishing ispracticed on the coat, a large dish-like portion D2 is created bydishing above the concave portions 90 b as shown in FIG. 9(b).Accordingly, when a wafer mark M including a line and space patternformed by periodically arranging convex portions 90 c as shown in FIG.9(c) is used, a large dish-like portion D3 is created by dishing abovethe wafer mark M. For this reason, an observed image of the wafer markis distorted when it is detected by the alignment system and accuracy ofalignment is reduced.

If the pattern formation surface (the upper most film formed of thepattern layer) is polished using the above mentioned substrate polishingapparatus, there is a problem that the thickness of the film,particularly, at a position between a pattern and the other patternadjacent to the former pattern becomes asymmetrical.

For example, in FIG. 12, there is provided with a polishing surfaceplate 122 that rocks leftward and rightward 300A with respect to thewafer 124 that rotates in response to the rotation of the rotary table126. However, since a relative polishing direction between the wafer andthe polishing pad becomes always constant, when the cross-section of thewafer 124 is observed, a polishing force (intensity of polishing) at aregion R_(1y), R_(2y) (hereinafter referred to as a region betweenpatterns) between a pattern Y₁ formed on the wafer 124 and otherpatterns Y₂, Y₃ adjacent to the pattern Y₁ offsets in the regionsR_(1y), R_(2y) between the patterns and therefore, the surface 124 a ispartially and deeply ground in said regions R_(1y), R_(2y), to cause thefilm thickness 34 b of the regions R_(1y), R_(2y) between the patternsto become asymmetrical.

If the film thickness of the upper layer film at a region between thepatterns constituting the alignment mark becomes asymmetrical, there isan occasion that a detecting position of the alignment mark isdisplaced.

SUMMARY OF THE INVENTION

The main object of the present invention is to provide an improvedexposure method which eliminates the defects of conventional exposingmethod as stated hereinbefore.

Another object of the present invention is to provide an exposure methodwhich does not create a dish-like portion on an alignment mark even whena flattening process is performed on the alignment mark (wafer mark).

A further object of the present invention is to provide a mask for usein the above method.

The further object of the present invention is to provide a polishingapparatus which can symmetrize the film thickness of every pattern whenthe film (particularly alignment mark) above the patterns is groundthereby.

An exposure method according to the present invention includes a firststep of forming on a substrate an alignment mark including a concave andconvex pattern, said mark being formed by the concave and convex patterndisposed with a pitch which is smaller than the predetermined valuebetween adjacent convex portions having a width of not less than apredetermined value; a second step of forming a coat over said alignmentmark and the other area on said substrate; a third step of flatteningsaid coat; and a fourth step of applying a photosensitive material onsaid coat flattened by said third step and projecting a mask patternthereto.

In one embodiment of the above exposure method, the distance betweensaid adjacent convex portions of said alignment mark having a width ofnot less than a predetermined value is not less than 2 μm.

A mask formed with an original pattern of alignment mark together with apattern to be transferred according to the present invention, isstructured such that the original pattern of said alignment mark isformed by disposing, between adjacent bright portions having a width ofnot less than a predetermined value, one or more bright patterns havinga width of less than said predetermined value with a pitch less thansaid predetermined value.

A mask formed with an original pattern of alignment mark together with apattern to be transferred according to the present invention, isstructured such that the original pattern of said alignment mark isformed by disposing, between adjacent dark portions having a width ofnot less than a predetermined value, one or more dark patterns having awidth less than said predetermined value with a pitch less than saidpredetermined value.

A substrate polishing apparatus according to the present inventionincludes a first holding member for holding a polishing member adaptedto polish the substrate; a second holding member for holding thesubstrate such that the surface on the substrate faces the polishingmember; a rotary member for relatively rotating said first holdingmember and said second holding member with respect to each other; and achange-over member for changing the direction of relative rotationbetween said first holding member and said second holding member.

According to the present exposing method, creation of dish-like portionson the alignment mark by dishing when the flattening process isperformed is prevented, since the width of an opening of a recess orconcave portion formed on the substrate is reduced by formingsub-patterns in an area or region which is conventionally a recessedportion. Thus no distortion of the mark is created and highly accuratealignment can be attained. In the exposing method according to thepresent invention, the distance between adjacent projections or convexportions of a main pattern of the alignment mark can be set to be notless than a resolution of the alignment sensor and the distance betweenadjacent projections or convex portions or depressions of thesub-pattern can be set to be not more than the resolution of thealignment sensor. Therefore, it is possible to effect alignment of thewafer mark in the same manner as a conventional method by means of aconventional alignment sensor using a bright and dark pattern in which amain pattern and a sub-pattern correspond to a bright portion and a darkportion, respectively.

Although dish-like portion is easily created between the convex portionsif the distance between adjacent convex portions, each having a width ofnot less than a predetermined value, of the alignment mark is not lessthan 2 μm, creation of dish-like portion is prevented by providing asub-pattern between the convex portions. An alignment sensor having aless resolution can be used for alignment of the wafer mark.

Moreover, the alignment mark exposed and transferred on the substratefrom the mask according to the present invention, includes thesub-pattern which is disposed between the adjacent convex portions ofthe main pattern having a width of not less than a predetermined valueand formed by a concave and convex pattern arranged with a distance ofnot more than the predetermined value. Therefore, creation of thedisk-like portions on the alignment mark is prevented and also creationof distortion in the mark is prevented, thereby enabling high precisealignment to be attained.

Since the substrate polishing apparatus according to the presentinvention includes the change-over member for changing a direction ofrotation, it is possible to change the direction of relative rotation ofthe first holding member and the second holding member while the surfaceof the substrate (the upper most layer formed on the upper potion of thepattern layer) is being polished.

Since the direction of rotation of the substrate is changed reverselywhile polishing, it is possible to prevent the cross-sectional shape inthe thickness of the film in an area between the patterns from becomingasymmetrical. Needless to say that the direction of rotation correspondsto the direction of polishing by the polishing member with respect tothe substrate and is relative to each other and therefore, the directionof rotation of the first and second holding member is not limited.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a relationship between FIGS. 1(a) and 1(b);FIG. 1(a) shows the first half of a flow chart explaining exposureoperation according to one embodiment of the present invention; and FIG.1(b) shows the second half of the flow chart.

FIG. 2(a) is a cross-sectional view of the wafer mark used in the aboveembodiment, and FIG. 2(b) is a plane view of the wafer mark.

FIG. 3 is a structural view showing a projection exposure apparatusadapted to be used in practicing the exposure method of the embodiment.

FIG. 4 is a structural view showing an alignment sensor of an LSA systemand a LIA system used in the projection exposure apparatus shown in FIG.3.

FIG. 5(a) is a plane view showing images of a circuit pattern andreticle mark exposed on the wafer; FIG. 5(b) is an enlarged plane viewof a part of FIG. 5(a); FIG. 5(c) is a plane view showing a patternarrangement of the reticle of the embodiment and FIG. 5(d) is anenlarged plane view showing a part of the reticle mark in FIG. 5(c).

FIGS. 6(a) to 6(c) are views showing other examples of wafer mark of theFIA system, FIG. 6(a) being an enlarged plane view showing wafer mark inwhich a minute sub-pattern is formed into a line-and-space pattern, FIG.6(b) being an enlarged plane view showing a wafer mark in which theminute sub-pattern is formed into a two dimensional check and FIG. 6(c)being an enlarged plane view showing a wafer mark in which thesub-pattern is formed into random dots.

FIG. 7 is an enlarged plane view showing an example of a wafer mark forthe LSA system.

FIGS. 8(a) and 8(b) are views explaining creation of a dish-like portionaccording to a prior art technique.

FIGS. 9(a) to 9(c) are views showing a state where the dish-like portionis created on the wafer mark of the prior art.

FIG. 10 is a schematic view showing a structure of one embodiment of thesubstrate polishing apparatus according to the present invention.

FIG. 11 is a view illustrating the main portion of the cross-section ofthe wafer polished by the substrate polishing apparatus according to thepresent invention.

FIG. 12 is a schematic view showing a structure of one example of aconventional substrate polishing apparatus.

FIG. 13 is a view illustrating the main portion of the cross-section ofthe wafer polished by the conventional substrate polishing apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the accompanying drawings, one embodiment of the presentinvention will be explained hereinafter.

FIG. 3 shows a schematic structure of a projection exposure apparatusadapted to be applied with the exposure method according to the presentinvention. In FIG. 3 an illumination light IL emitted from a highpressure mercury-vapor lamp 1 is reflected by an elliptical mirror 2 andis once collected at a second focal point, and thereafter enters into anillumination optical system 3 including a collimator lens, aninterference filter, an optical integrator (fly-eye lens), and anaperture stop (σ stop). Although the fly-eye lens is not shown, it isarranged within a plane perpendicular to an optical axis such that afocal surface thereof at a side of the reticle coincides with a Fouriertransform surface (a pupil conjugate surface).

There is disposed adjacent to the second focal point of the ellipticalmirror 2 a shutter (for example a rotary shutter having four blades)which closes and opens a passage of the illumination light IL by a motor38. A laser beam such as the excimer laser (KrF excimer laser, ArFexcimer laser) and the like, or high harmonic wave such as metallicvapor laser or a YAG laser may be used as the illumination light forexposure other than the high pressure mercury-vapor lamp 1.

In FIG. 3, most of the illumination light (such as an i beam and thelike) emitted from the illumination optical system 3 and having awavelength band to which a photoresist is sensitive is reflected by abeam splitter 4 and then come to a mirror 8 after passing through afirst rely lens 5, a variable field stop (reticle blind) and a secondrely lens 7. The illumination light reflected by a mirror 8 insubstantially downward direction which is perpendicular to the opticalaxis of the illumination light illuminates with uniform illuminance apattern area of the reticle R through a main condenser lens 9. A surfaceon which the reticle blind 6 is arranged is in conjugate relationship(image formation relationship) with a pattern formation surface of thereticle R and an illumination field of the reticle R can be optionallyset by opening and closing a plurality of movable blades constituting areticle blind by means of a drive system to change the size and theshape of an opening.

It is presumed that a Z axis is parallel with the optical axis AX of theillumination optical system which intersects the reticle R, an X axis isin a plane perpendicular to the Z axis and is parallel with a surface ofthe paper of FIG. 3 and a Y axis is perpendicular to the surface of thepaper of FIG. 3.

FIG. 5(c) shows the reticle R according to the present embodiment. Inthe reticle R shown in FIG. 5(c), reticle marks 64X and 64Y are formedas alignment marks at substantially central positions of two sections ofa shading band 62 which surrounds a pattern area or region 61. The twosections of the shading band intersect each other at a right angle. Animage of the reticle marks are formed on the substrate or wafer W aswafer marks having a concave and convex pattern by projecting the imageof the reticle marks onto the wafer and developing it. These reticlemarks 64X and 64Y may be commonly used as alignment marks when theposition of each shot area of the wafer W and the position of thereticle R is aligned or registered. These two reticle marks 64X and 64Yhave the same structure (direction, thereof is different from eachother), each of which is formed by means of a shading film or coating ofchromium or the like positioned within transparent windows 63X and 63Yformed in the shading band 62. Moreover, the reticle R has two alignmentmarks 65A and 65B which are formed near outer periphery thereof inopposite relation and consist of two cross-like shading marks. These twoalignment marks 65A and 65B are used for aligning the reticle R(alignment of the position with respect to the axis of light).

Referring to FIGS. 5(c) and 5(d), reticle marks on the reticle R will beexplained in detail hereinafter.

As shown in FIG. 5(c), the reticle marks consist of a reticle mark 64Xfor detecting the position in a X direction and a reticle mark 64Y fordetecting the position in a Y direction. These reticle marks 64X and 64Yare constituted by five sub-marks disposed in a transparent ortransmittivity portion. The reticle mark 64Y for detecting the positionin the Y direction is turned 90° with respect to the reticle mark 64Xfor detecting the position in the X direction.

FIG. 5(d) shows a part of the structure of the reticle mark 64X for theX direction. In FIG. 5(d), the reticle mark 64x is structured bypositioning, between adjacent transmittivity portions 66A, 66B, . . . ,each having a width in the X direction of not less than a predeterminedvalue, sub-marks 67A, 67B, . . . , each having the same width as that ofthe transmittivity portion. Each sub-mark 67A, 67B, . . . , isconstituted by alternately disposing five slit-like shading films ormembranes 68 and four transmittivity portions 69 with a predetermineddistance in the X direction.

These sub-marks 67A, 67B, . . . , are spaced apart from each other witha distance of not less than a predetermined value. This distance,preferably, is determined considering a resolution of the alignmentsensor. The distance between adjacent two sub-marks is determined sothat a distance between two adjacent sub-patterns of the wafer markformed on the wafer after sub-marks 67A, 67B, . . . , on the reticle areexposed and transferred to the wafer, is not less than 2 μm. The shapeof the sub-marks 67A, 67B, . . . , is not limited to that shown in FIG.5(d). The reticle marks 64X, 64Y may be marks in which bright portionsand dark portions are reversed.

The pitch distance between adjacent shading films 68 and the pitchdistance between adjacent transmittivity portions 69 in the sub-marks67A, 67B, . . . , are determined so that an image of the sub-marksbecomes a size of not more than the resolution of the alignment sensorwhen the sub-marks are transferred onto the wafer. Although thesub-marks 67A, 67B, . . . , in the reticle mark 64X, according to thepresent embodiment is a regular pattern, they may be an irregularpattern. However, the distance between adjacent bright portions or thedistance between adjacent dark portions in the irregular pattern are,preferably, determined so that an internal structure of a sub-pattern onthe wafer formed by the sub-marks has a fineness of not more than theresolution of the alignment sensor used for detecting the sub-patternwhen the sub-marks are transferred onto the wafer. The reticle marks 64Xand 64Y can be formed by a well known pattern generator or an electronbeam drawing device.

Referring again to FIG. 3, the reticle R is set on a reticle stage RSwhich is precisely controlled, the movement thereof in the direction (Zdirection) along an optical axis AX (this axis coincides with an opticalaxis of the illumination optical axis) of the projection optical system13. The reticle stage is also two-dimensionally movable and rotatablelittle by little in the horizontal plane which is perpendicular to theaxis AX. The rotation of the reticle stage is precisely controlled.Disposed and fixed on an end of the reticle stage RS is a movable mirror11m which reflects a laser beam from a laser interferometric measuringmachine (laser interferometer). The position of the reticle stage RS isalways detected with resolving power, for example, in the order of 0.01μm by the laser interferometer. Disposed above the reticle R are reticlealignment systems (RA systems) 10A and 10B which detect two cross-shapedalignment marks 65A and 65B formed on the reticle adjacent to the outerperiphery thereof. The reticle R is positioned so that the center pointof a pattern area 61 coincides with the optical axis AX of theprojection optical system 13 by slightly moving the reticle stage RS onthe basis of measured signals from the RA system 10A and 10B.

The illumination light IL having passed through the pattern area 61 ofthe reticle R enters into the projection optical system 13 which isdouble telecentric and the projected image of a circuit pattern of thereticle R which is reduced into ⅕ times by the projection optical systemis formed, in superimposed relation, in one of shot areas on the waferwhich has a photoresist layer on the surface thereof and is held suchthat the surface of the photoresist coincides with the best imageformation surface of the projection optical system.

The wafer W is held by a vacuum suction on a wafer holder (not shown),which is rotatable. The wafer stage WS is structured so that it can movetwo dimensionally in step-and-repeat method by a motor 16. The waferstage WS is stepped to the next shot position after transfer exposure ofthe reticle R for one shot area on the wafer W is finished. Disposed andfixed on one end of the wafer stage WS is a movable mirror 15 whichreflects a laser beam from a laser interferometer 15. Thetwo-dimensional coordinates of the wafer stage WS is always detectedwith a resolving power, for example, in the order of 0.01 μm by thelaser interferometer 15. The laser interferometer 15 measurescoordinates of an X direction and a Y direction of the wafer stage WS. Astage coordinate system (a stationary coordinate system) (X,Y) of thewafer stage WS is determined by the coordinates in the X direction andthe Y direction. Namely, coordinate values of the wafer stage WSmeasured by the laser interferometer 15 are the coordinate values on thestage coordinate system.

A reference member (glass substrate) having a reference mark which isused when base line value (the distance between the reference point andthe center of exposure of the alignment sensor) is measured is disposedon the wafer stage WS so that the level of the reference member is thesame as the level of an exposure surface of the wafer W.

Provided for the projection exposure apparatus shown in FIG. 3 is animage formation characteristic compensator 19 capable of adjusting animage formation characteristic of the projection optical system 13. Theimage formation characteristic compensator 19 according to the presentembodiment compensates the image formation characteristic, for exampleprojection magnification or distortion of the projection optical system13 by independently moving (movement in the direction parallel with theoptical axis AX or inclination) a part of lens elements, particularlyeach of a plurality of lens elements near to the reticle R, constitutingthe projection optical system 13 using a piezoelectric-crystal elementsuch as a piezo element.

Provided at one side of the projection optical system 13 is an alignmentsensor (hereinafter referred to as “Field Image Alignment system (FIAsystem)”) which image-processes by an off-axis method. In thisembodiment, detection of the position of the wafer mark is performed bythis FIA system. In this FIA system, a light emitted from a halogen lamp20 is introduced into an interferometer 23 through a condenser lens 21and an optical fiber 22. The light having a wavelength band to which thephotoresist layer is sensitive and an infrared wavelength band is cutoff in the interferometer 23. The light having been passed through theinterferometer 23 enters into an objective lens 27 of double telecentrictype through a lens system 24, a beam splitter 25, a mirror 26 and afield stop BR. Light having emitted from the objective lens 27 isreflected by a prism (or mirror) 28 fixed on the periphery of the lowerportion of a lens barrel so that an illumination field of the projectionoptical system 13 is not shaded, and irradiates the wafer W in thedirection substantially perpendicular to the surface of the wafer.

The light from the objective lens 27 is irradiated to a partial regionincluding the wafer mark on the wafer W and light reflected from thepartial region is introduced to a collimator mark or indicator plate 30through the prism 28, the objective lens 27, the field stop BR, themirror 26, the beam splitter 25 and a lens system 29. The indicatorplate 30 is disposed in a plane which is conjugate with the wafer Wrelative to the objective lens 27 and the lens system 29, an image ofthe wafer mark on the wafer W is formed in a transparent window. Formed,in the transparent window of the indicator plate 30 is an indicator markwhich is formed by disposing two rectilinear marks extending in the Ydirection and spaced in the X direction with a predetermined distance.The light having passed through the indicator plate 30 is introduced toan image pickup element (CCD camera and the like) through a first relaylens system 31, a mirror 32 and a second relay lens system 33 and animage of the wafer mark and an image of the indicator mark are formed ona light receiving surface of the image pickup element. An image pickupsignal SV from the image pickup element 34 is supplied to a main controlsystem 18 wherein the position (a coordinate value) of the X directionof the wafer mark is calculated. Another FIA system (FIA system for a Yaxis) for detecting the position of the wafer mark in the Y direction isprovided other than the above mentioned FIA system (FIA system for a Xaxis), although it is not shown in FIG. 3.

There is provided at one side of an upper portion of the projectionoptical system 13 with an alignment sensor of a TTL (through the lens)system and the light from the alignment sensor 17 for detecting theposition of the wafer mark is introduced into the projection opticalsystem through mirrors M1 and M2. The light for detecting the positionis irradiated to the wafer mark on the wafer W through the projectionoptical system and the reflected light from the wafer mark is returnedto the alignment sensor 17 through the projection optical system 13, themirror M3 and the mirror M2. The position of the wafer mark on the waferW is obtained from a signal obtained by photoelectrically converting thereflected light returned to the alignment sensor 17.

FIG. 4 shows the detailed structure of the alignment sensor 17 of theTTL system shown in FIG. 3. In FIG. 4, the alignment sensor 17 accordingto this embodiment is that constituted by combining an alignment systemof a two-beam interference system (hereinafter referred to as “LIAsystem”) and an alignment system of laser step alignment system(hereinafter referred to as “LSA system”) with their optical membersbeing shared as many as possible. The structure of the alignment sensor17 will be briefly explained herein, but the detailed structure is shownin Laid Open Patent Publication No. Hei 2-272305.

In FIG. 4, a laser beam emitted from a light source (He-Ne laser sourceand the like) 40 is split by a beam splitter 41. A laser beam reflectedby this beam splitter 41 enters into a first beam formation opticalsystem (LIA optical system) 45 through a shutter 42. On the other handthe laser beam having passed through the beam splitter 41 enters into asecond beam formation optical system (LSA system) 46 through a shutter43 and a mirror 44. Accordingly, the LIA system and the LSA system canbe selectively used by suitably driving the shutters 42 and 43.

The LIA system 45 includes two sets of acousto-optic modulators andemits two laser beams having a predetermined frequency differential Δfsymmetrically with respect to the optical axis. The two laser beamsemitted from the LIA system 45 reaches to a beam splitter 49 through amirror 47 and a beam splitter 48. Two laser beams passed through thebeam splitter enter and form an image (cross) on a diffraction grating55 for reference which is fixed on the exposure apparatus from twodifferent directions which cross each other with a predetermined angle,through a lens system (a reverse Fourier transform surface) 53 and amirror 54. A photoelectric detector or sensor 56 receives interferedlight of diffracted light generated in the same direction when lightpassed through the diffraction grating 55 and output the photoelectricsignal RS having a sine wave corresponding to the intensity ofdiffracted light to a LIA operation unit 58 in the main control system18 (see FIG. 3).

On the other hand, two laser beams reflected by the beam splitter 49once cross each other at an opening of the field stop 51 by theobjective lens 50 and then enter into the projection optical system 13through the mirror M2 (in FIG. 3 mirror M1 is omitted). The two laserbeams entered into the projection optical system 13 once converge as aspot substantially symmetrical with respect to the optical axis AX on apupil surface of the projection optical system 13 and then becomes beamswhich incline each other on both sides of the optical axis AX with asymmetrical angle with respect to a pitch direction (Y direction) of thewafer mark on the wafer W, thereafter enter to the wafer mark from thetwo different directions with a predetermined crossing angle. Formed onthe wafer mark are one-dimensional interference fringes which move witha speed corresponding to the frequency differential. Plus or minus (±)one-dimensional diffracted light generated in the same direction fromthe mark, i.e., in the direction along the optical axis, is received bythe photoelectric detector 52 through the projection optical system 13and the objective lens 50. The photoelectric detector 52 outputs thephotoelectric signal SD having sine wave corresponding to cycle ofchange in bright and dark of the interference fringes to the LIAarithmetic processing unit 58. The LIA arithmetic processing unit 58calculates a positional offset or displacement value of the wafer markfrom the phase difference in waves of the two photoelectric signals SRand SDW, and uses a positional signal PDs from the laser interferometer15 to obtain a coordinate position of the wafer stage WS when the abovepositional offset value becomes zero.

The LSA optical system 46 includes beam expander, cylindrical lens andthe like. The laser beam emitted from the LSA optical system 46 entersinto the objective lens 51 through the beam splitter 48 and 49.Moreover, the laser beam exited from the objective lens 50 onceconverges into a slit-like shape at an opening of the field stop 51 andthen enters into the projection optical system 13 through the mirror M2.The laser beam entered into the projection optical system 13 passesthrough a substantially central portion of the pupil surface andthereafter is projected on the wafer W as elongated band-like spot lightwhich extends in the X direction in an image field of the projectionoptical system and faces toward the optical axis AX.

When the spot light and the wafer mark (a diffraction grating) on thewafer W are moved with respect to each other in the Y direction, thelight emitted form the wafer mark is received by the photoelectricdetector 52 through the projection optical system and the objective lens50. The photoelectric detector 52 photoelectrically converts only plusor minus (±) first to third diffracted lights among lights from thewafer mark, and photoelectric signal SDi thus obtained by thephotoelectric conversion and corresponding to intensity of the light isoutputted to the LSA arithmetic processing unit 57 in the main controlsystem. The LSA arithmetic processing unit 57 is provided with thepositional signal PDs from the laser interferometer 15 and samples thephotoelectric signal SDi in synchronized with an up-down pulse generatedevery unit displacement of the wafer stage WS. The LSA arithmeticprocessing unit 57 converts sampled values into digital values andmemorizes in a memory in the order of addresses, thereafter calculatesthe position in the Y direction of the wafer mark by predeterminedarithmetic processing. The alignment sensor for the X direction fordetecting the position of the wafer mark of the LIA system for the Xdirection and the position of the wafer mark of the LSA system may beadditionally provided.

One example of the exposure operation according to the present inventionwill be explained with reference to a flow chart shown in FIG. 1.

First of all, in a step 101 shown in FIG. 1, a photoresist is applied tothe wafer W by means of an unshown coater and they are baked as occasiondemands. In a step 102, the baked wafer W is loaded on the wafer stageWS of the projection exposure apparatus shown in FIG. 1 and the reticleR shown in FIG. 5 is loaded on the reticle stage RS. Next, in a step103, a circuit pattern and reticle marks 64X, 64Y in the pattern area 61on the reticle R in FIG. 5(c) is projected with a reduction of ⅕ timeson a photoresist layer applied to the wafer W through the projectionexposure system 13. Due to this, an image of the circuit pattern isprojected in a shot area SA on the wafer W and an image 70X of thereticle mark 64X and an image 70Y of the reticle mark 64Y are projectednear the shot area SA as shown in FIG, 5(a). For example, the image 70Xof the reticle mark 64X is constituted by separately arranging images ofsub-marks 71A, 71B, . . . , 71E with the predetermined pitch along the Xdirection as shown in FIG. 5(b). These images 70X, 70Y of the reticlemarks become wafer marks consist of a concave and convex pattern after aprocess such as development.

The wafer W on which images of the circuit pattern and the reticle marks64X, 64Y on the reticle R are transferred is developed in a step 104. Ina step 105, after a baking process is finished the wafer W is etchedusing a resist pattern as a mask and then is washed as occasion demands.A developing device used in the step 104 may adopt a spray method inwhich a predetermined cleaning agent and developing agent are sprayed orejected to an object in the form of a spray or a shower, or a dip methodin which the object is dipped within the developing agent and thecleaning agent for a predetermined time interval, respectively, anddeveloped. The wafer is developed and washed by either of the abovemethods. Although an etching process may be performed by means of a wetmethod or a dry method, at present the dry method is used. In order topractice this dry etching, for example, a plasma etching device is used.

In the step 105, completion of etching is detected by a laser beaminterferometry using a spectral analysis method or a optical reflection,an ellipsometric method, a grating optical diffraction method and thelike. After confirming the completion of the etching the wafer W iswashed as occasion demands. A resist layer and a useless oxide filmportion or metallic film portion are removed as described above and, asshown in FIG. 2(b), the necessary circuit and wafer mark are formed intoa concave and convex shape in a coat 73 on a coat (hereinafter referredto as circuit pattern layer) 72 on the wafer W. The wafer mark 76X isformed by an image on the wafer W which is transferred, with a rate ofreduction, from the reticle mark 64x for the X axis through theprojection optical system PL.

FIG. 2 shows a wafer mark formed in accordance with the presentinvention, that is the wafer mark 76X which is formed on the wafer W bytransferring the reticle mark 64X thereto. This FIG. 2 shows a layer tobe flattened and made of an insulating film (a metallic film) to beexplained later and is used when a flattening process is explained. FIG.2(a) is a cross-sectional view of the wafer mark 76X for the X axisviewed along the Y axis and FIG. 2(b) is a plane view of the wafer mark76X.

As shown in FIGS. 2(a) and 2(b) the wafer mark 76X is formed togetherwith the circuit in the coat 73 formed on the coat 72 as explainedabove. The coat 73 is formed into projections or convex portion 73 a, 73b on opposite sides, a plurality of projections or convex portions 75Ato 75D separately arranged between the convex portions 73 a and 73 awith a distance of not less than a predetermined value and sub-patterns74A to 74E each of which is made by a minute concave and convex patternconsist of projections or convex portions 78 and recesses or concaveportions 77. The width P1 of each sub-pattern and the width P2 of eachconvex portion 75A-75D have a predetermined size, respectively (in thisembodiment P1 and P2 are about 6 μm, respectively). The width P3 of eachprojection or convex portion and each recess or concave portion of thesub-patterns has a predetermined size, and in this embodiment P3 isabout 0.67 μm. However, this width P3 is not limited to the above valueif it is such a size as the sub-pattern is detected and processed as adark portion of the alignment sensor to be used. Although, in thisembodiment the distance (that is the width of sub-pattern) P1 betweenadjacent convex portions of the mark 76X is about 6 μm, this distance orwidth is not limited to this value, if it is not less than theresolution of the alignment sensor. Preferably, the distance P1 is notless than 2 μm if possible. Since the sub-patterns 74A to 74E of thealignment sensor formed as explained above can not be resolved by a marksensor of the FIA method, it is possible to process them as a bright anddark pattern in which the convex portions 75A to 75D of the wafer mark76X are processed as bright portions and the sub-patterns 74A to 74E areprocessed as dark portions. The wafer mark Y is formed in the samemanner as the wafer mark X.

As explained above, the surface on the wafer in which the predeterminedcircuit and the wafer mark 76X, 76Y are formed is flattened still morein order to form an upper layer circuit in steps 106 and 107. Thisflattening operation may be performed in the same method as explainedbefore, however, according to this embodiment, in the step 106 ainsulating film or membrane (or a metallic film or membrane, hereinafterreferred to as a film to be flattened) 79 of an oxide silicon (SiO₂) andthe like is coated. In this stage, there are minute concave portions andconvex portions in a surface 79 a of the film to be flattened 79. Nextin the step 107, a process for chemically and mechanically grinding orpolishing the surface 79 a of the film to be flattened is practiced.This chemical and mechanical polishing is a method for mechanicallypolishing or grinding the surface of the film to be flattened addingpredetermined chemicals or water as occasion demands.

FIG. 10 shows a schematic structure of one embodiment of a substratepolishing or grinding apparatus according to the present invention. Inthis embodiment there is shown the substrate polishing or grindingapparatus having a structure in which only a vacuum suction table 116for holding the wafer is rotatable, that is the substrate polishingapparatus having a structure in which the vacuum suction table 116 forholding the wafer 115 is disposed on a rotary table 117 and a polishingor grinding surface plate 113 having a polishing or grinding pad 114 isheld by a rocking or oscillating table 112.

The rocking table 112 rocks or oscillates in right and left directionsand the speed of rocking motion thereof is controlled to a predeterminedvalue determined by a controller 111. The rocking table 112 holds thepolishing surface plate 113 and this polishing surface plate 113 isprovided with a polishing pad 114 facing a face 115 a (hereinafterreferred to as a pattern formation surface) of wafer on which a patternlayer and an upper film are formed.

The wafer is held by suction by means of the vacuum suction table 116with the pattern formation surface 115 a which is a surface to bepolished or ground facing above. Since this vacuum suction table 116 isdisposed on the rotary table 117 which is rotatable in reciprocaldirections, the wafer 115 is rotatable in the reciprocal directions.

The direction of rotation 100B of the rotary table 117 is controlled sothat it is reversed every predetermined times determined by thecontroller 111. In this embodiment a set-up time which is a unit forreversing the direction of rotation of the rotary table 117 can beoptionally set by the user. For example, in the case where 20 minutesare needed as a processing time for the pattern formation surface 115 athe set-up time may be set such that the rotary table rotatesright-wards for 10 minutes and then in left-wards for 10 minutes or maybe set with time difference such that the rotary table rotatesright-wards for 8 minutes and then in left-wards for 12 minutes, ifextent of progress of asymmetry of the cross-section in the regionbetween the patterns differs in relation to the direction of rotation.

Moreover, in the case where extent of progress of asymmetry of thecross-section in the region between the patterns does not differ inrelation to the direction of rotation, for example if direction ofrotations is changed between right-ward rotation and left ward rotationevery one or more minutes or every one or more revolutions of the rotarytable, a wafer having a complete symmetrical cross-section of patterncan be obtained, since the time at which the rotary table rotates in onedirection is short thereby reducing extent of progress of asymmetry.

In this embodiment the substrate polishing apparatus is structured suchthat the speed of rotation and the speed of rocking motion of the rotarytable 117 is controlled by the controller 111. Therefore, finishing timeand finishing state of polishing of the pattern formation surface of thewafer 115 can be controlled by controlling rotation and rocking motionof the rotary table by means of the controller in response to commandsof the set-up time and the speed of rotation set by the user.

Furthermore, the pattern formation surface 115 a of the wafer is wellpolished by injecting the polishing agent between the pattern formationsurface 115 a and the polishing pad 114 from the polishing agentsupplying nozzle 118 and by moving at least one of the vacuum suctiontable 116 and the polishing surface plate 113 in up and down direction100 c by means of instructions from the controller 111 to contact thepolishing pad 114 moving in response to the rocking motion of thepolishing surface table 113 and the wafer rotating in response torotation of the rotary table 117.

In the above explained embodiment the vacuum suction table 116 isrotated and the polishing surface plate 113 is rocked or oscillated.However, same technical advantages as explained above is obtained byrotating the polishing surface plate 113 and rocking or oscillating thevacuum suction table 116. Moreover, the same technical advantage asexplained above is obtained by a structure in which the vacuum suctiontable 116 and the polishing surface plate 113 are rotatable.

FIG. 2(a) shows the wafer W, particularly the state of a surface 80 ofthe film 79 on the wafer W, which is flattened by the method explainedabove. The surface 80 of the film to be flattened 79 does not sink abovethe wafer mark 76X and form a smooth plane. This is because no recessesor concave portions having a width of not less than 2 μm are formedbetween the adjacent convex portions among the convex portions 76A to76D by positioning minute sub-patterns 74A to 74E in the spaces betweenthe adjacent convex portions and flatness of the film to be flattened 79above the wafer mark 76X can be obtained.

In a step 108, a photoresist is applied again on the wafer W having afilm to be flattened 79 the surface of which is flattened by the processexplained above. In this case, for example, a photoresist applyingdevice (coater) of a spin coat method in which thin film of thephotoresist is formed on the wafer W by using centrifugal force is used.The wafer W on which the photoresist is applied is set on the waferstage of the above mentioned projection optical system, a projectionoptical system adapted to practice the exposure method according to thepresent embodiment or a conventional pattern formation device. At thistime the wafer marks 76X, 76Y are detected by the alignment sensor ofthe FIA system through flattened film and alignment of the wafer isperformed.

In the wafer mark of the LSA system or the LIA system, detection andalignment of the wafer mark can be performed same as that of the FIAsystem by using alignment sensor for the LSA system or the LIA system.

Again, in a step 110, a new circuit pattern and, if occasion demands, anew wafer mark are formed using another reticle. At this time, in aposition at which the new wafer mark is formed there is no dish-likeconcave portion due to dishing phenomenon explained before and a stablewafer mark having no mark distortion is formed on the surface 80 of thefilm to be flattened 79 on the wafer.

FIGS. 6(a) to 6(c) show another embodiment of a wafer mark for the Xaxis of the FIA system which is used in the exposure method according tothe present invention. FIG. 6(a) shows a wafer mark of a line-and-spacepattern which is formed by arranging minute sub-patterns along thenon-measuring direction. This wafer mark is constituted by line marks81A, 81B and 81C each of which consists of a plurality of projections orconvex portions 83 and a plurality of recesses or concave portions 82having a width not more than a predetermined value. The line marks 81A,81B and 81C are formed by alternately and separately arranging theconcave portions 82 and convex portions 83 with a predetermined pitch inthe Y direction. FIG. 6(b) shows a wafer mark in which minutesub-patterns are two-dimensional lattice shape. This wafer isconstituted by line marks 84A, 84B and 84C each having minutelattice-shaped concave and convex pattern. The line marks 84A, 84B and84C are separately arranged with a distance of not less, than apredetermined value in the same manner as the line marks shown in FIG.6(a). FIG. 6(c) shows a wafer mark in which minute sub-patterns arerandom dots shape. This wafer is constituted by line marks 85A, 85B and85C each having dot-shaped projections or convex portions which arerandomly arranged. The line marks 85A, 85B and 85C are separatelyarranged with a distance of not less than a predetermined value in thesame manner as the line marks shown in FIGS. 6(a) and 6(b). Thesealignment marks having minute sub-patterns can be used not only in theFIA system but also in the LSA system, the LIA system and the like.

The line marks (81A, 81B or 81C), the line marks (84A, 84B or 84C) andthe line marks (85A, 85B and 85C) which are explained above correspondto one of sub-patterns (74A, 74B, 74C, 74D or 74E) of the wafer mark 76Xshown in FIG. 2(b), and therefore the former may be used in place of thelatter.

FIG. 7 shows a wafer mark for the LSA system. This wafer mark includes apattern 86A which is a combination of a plurality of minute sub-patterns87 each of which consists of a slit-shaped convex and concave pattern inwhich slits extend along the X axis and a plurality of projections orconvex portions 88, and a pattern 86B which is a combination of aplurality of minute sub-patterns 87, 89 each of which consists of aminute convex and concave pattern which extend along the Y axis and aplurality of projections or convex portions 88. Wafer marks other thandescribed above can be used in the exposure method according to thepresent invention.

The exposure method according to the present invention can also be usedin an exposure apparatus of a step-and-scan method wherein exposure isperformed scanning the reticle and wafer at the same time. Thus, thescope of the present invention is not limited to the above embodimentsand it is possible for those skilled in the art to take manymodifications within the scope of the present invention.

According to the exposure method no dishing phenomenon is created abovethe alignment mark even after a flattening process is performed.Accordingly, the creation of distortion in the detected light of thealignment mark is prevented when the alignment of the wafer is performedto increase the accuracy of alignment. Moreover, it is not necessary tomodify a mechanism in an exposing and transferring apparatus andtherefore the structure thereof is simple.

In the case where the distance between adjacent convex portions ofalignment mark is not less than 2 μm, the alignment mark can be detectedby means of a conventional alignment sensor having ordinal resolution.If the distance between adjacent convex portions of the alignment markis not less than 2 μm, it is easy to create dishing phenomenon, butaccording to the present invention, creation of dishing is prevented.

Moreover, dishing is prevented from creating in the above alignment markmade by exposing and transferring mark using a mask according to thepresent invention. This prevents creation of distortion of marks andenables highly precise alignment.

Furthermore, according to the substrate polishing apparatus of thepresent invention the film can be polished so that the film thickness ofeach pattern becomes symmetrical. Namely, as is clear from FIG. 11, apolishing force (intensity of polishing) in regions R_(1x), R_(2x)(hereinafter called as regions between patterns) between a pattern X₁formed on the wafer 115 and other patterns X₂, X₃ adjacent to thepattern X₁ do not deviate in one direction in the regions R_(1x),R_(2x), and the surface 115 a of the wafer 115 is grounded symmetricallyin the regions R_(1x), R_(2x) thereby making the film thickness 115 bsymmetrical. If patterns X₁, X₂ and X₃ constitutes an alignment mark,the surface of film in the regions R_(1x), R_(2x) between patterns sinkssymmetrically. This reduce effects on detection of alignment mark.

While the invention has been particular shown and described in referenceto preferred embodiments thereof, it will be understood by those skilledin the art that changes in form and details may be made therein withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A mask including: a plurality of first lightsealed patterns arranged with a predetermined interval so as to form analignment mark on the substrate; and a plurality of second light sealedpatterns disposed between adjacent first light sealed patterns with aninterval which is less than said predetermined interval.
 2. An exposuremethod comprising: using the mask as set forth in claim 1 and forming analignment mark on said substrate by projecting an alignment mark on saidmask onto said substrate.
 3. An exposure apparatus for exposing asubstrate by projecting a pattern on a mask onto the substrate,comprising: a mask holding member which holds the mask as set forth inclaim 1, and a projection system which projects an alignment mark on themask onto the substrate.
 4. A mask including: a plurality of first lighttransparent areas which are spaced apart from each other with apredetermined distance so as to form an alignment mark on the substrate;and a plurality of second light transparent areas, each of which isdisposed between adjacent first light transparent areas with a distanceof less than said predetermined distance.
 5. An exposure methodcomprising: using the mask as set forth in claim 4 and forming analignment mark on said substrate by projecting an alignment mark on saidmask onto said substrate.
 6. An exposure apparatus for exposing asubstrate by projecting a pattern on a mask onto the substrate,comprising: a mask holding member which holds the mask as set forth inclaim 4; and a projection system which projects an alignment mark on themask onto the substrate.
 7. An exposure apparatus comprising: aprojection optical system which projects an image of a mark on a maskonto a substrate to form an alignment mark on said substrate; and analignment sensor which detects said alignment mark formed on saidsubstrate; wherein said alignment mark includes a plurality of firstpatterns having a height with a predetermined interval and a pluralityof second patterns having a height with an interval of less than saidpredetermined interval between adjacent first patterns.
 8. An exposureapparatus according to claim 7, wherein the distance between each of aplurality of said second patterns is less than resolution of saidalignment sensor.
 9. An exposure apparatus according to claim 8, whereinsaid second patterns are regular.
 10. An exposure apparatus according toclaim 8, wherein said second patterns are irregular.
 11. An exposureapparatus according to claim 7, wherein the distance between adjacentfirst patterns is equal to or more than 2 μm.
 12. An exposure apparatusaccording to claim 7, wherein said alignment sensor includes analignment system of an image processing type which picks up an image ofsaid alignment mark to measure the position of said alignment mark. 13.An exposure apparatus according to claim 7, wherein said alignmentsensor includes an alignment system of an interference type whichmeasures the position of said alignment mark by using interference oflight from said alignment mark.
 14. A mask comprising: a circuit patternarea having circuit patterns; and a mask mark formed in thepredetermined positional relationship with said circuit pattern area,the mask mark including a plurality of sub-marks which are arranged oneby one with predetermnined interval therebetween, said sub-marksincluding a plurality of patterns.